1. Field of the Invention
This invention relates, in general, to communication systems and, more specifically, to systems for communicating between electrical power customer locations and a control center.
2. Description of the Prior Art
Power line communication systems are used to convey various information between different locations in an electrical power distribution system. One type of communication system of growing importance is a system which transfers information between a central control station and the customer load location. Such a system can be used to selectively control the power consumption at the customer location, interrogate the customer's metering facility to produce signals which are responsive to the energy used, or for any other purpose requiring two-way communication facilities.
Conventional two-way communication facilities are bidirectional in nature. That is, they are capable of conveying information over the same route in both directions between the customer location and the central control station. This requires communication components of considerable complexity to provide adequate two-way transmission. Therefore, it is desirable, and it is an object of this invention, to provide a communication system for electrical power systems which requires relatively simple components capable of one-way transmission.
Many conventional power line communication systems use a portion of the power line to transmit or convey the signals between two different locations in the power distribution system. A problem exists with such systems when the communication signals are used to sectionalize or control the route over which the electrical power is conveyed. During a line fault or other condition in which the power transmission line has been interrupted or severely loaded, it becomes very impractical to receive carrier communication signals impressed upon the transmission or distribution line. Consequently, at the very time when control functions are necessary, such communication systems are not effective in controlling the load applications to the power system. Therefore, it is also desirable, and it is another object of this invention, to provide a communication system for electrical power systems which provides selective load and control switching regardless of the condition of the transmission and distribution lines.
Conventional power system communication systems which are not susceptible to line faults usually involve the use of telephone lines or radio facilities to transmit information and control signals to the remote locations along the power system. The use of telephone lines provides continuity even when the transmission or distibution lines are discontinuous. However, such telephone lines are relatively uneconomical for this type of service and are still susceptible to outage due to broken lines, which may occur simultaneously with the power lines if the cause of the outage is due to the failure of a common supporting structure for both lines.
Using radio facilities overcomes the problems associated with communications to a switching location positioned, for instance, at a customer location. However, the use of such radio facilities has not proven to be extremely practical since the power output of such facilities is relatively low and a considerable number of transmitting facilities must be provided to ensure sufficient coverage. In addition, the receiving apparatus associated with such radio systems is manufactured on a relatively low volume basis and is comparatively expensive. Therefore, it is also desirable, and it is another object of this invention, to provide a communication system for electrical power systems which can still control the application of a load at a customer location when either the telephone lines or the electrical lines are damaged, which uses radio facilities having sufficient power and coverage to effectively make such use economical, and which uses conventional radio receiver technology and the economical benefit of high production assemblies to make the cost of the receiver practical.